Overtravel control mechanism for stepping switches



Jan. 21, 1969 w. w. WRIGHT 3,422,691

OVERTRAVEL CONTROL MECHANISM FOR STEPPING SWITCHES Filed Oct. 5. 1966 IN VEN TOR W/LL/AM W IVR/GHT 3 3 2 I l 0 3 3 H O 3 C 2 A TTORNE Y5United. States Patent 8 Claims This invention relates generally toelectromagnetically operated switches or relays and, more particularly,to incremental motion, multi-position switches known as steppingswitches.

In the conventional stepping relay, an electromagnet is employed todrive a pawl which engages with a toothed ratchet wheel, the ratchetbeing advanced by a single increment each time the electromagnet isenergized. It is often desirable that the stepping switch be capable ofvery rapid operation, particularly in those applications where theswitch must have the ability to be advanced by several increments in avery short period of time. The moving parts of such a switchingmechanism must accordingly be subjected to rapid acceleration. Inconsequence, at the instant the necessary motion is completed, theseparts are moving at a relatively high velocity. It is then necessary tostop further rotation of the ratchet wheel in order to maintain the newposition and to return the remaining moving parts to their initialposition in preparation for the next operation.

It is a general object of the present invention to absorb the kineticenergy of the moving parts in a stepping switch and to prevent inertialovertravel of the moving ratchet wheel.

Overtravel control devices employed in prior stepping switches havenormally taken the form of rigid stops positioned in the path of one ormore moving parts for blocking forward motion beyond a predeterminedpoint. In these arrangements, a high pressure impact takes place at theend of each stroke since the moving parts which must be stopped aremoving at maximum velocity. As the switch is operated, these repeatedimpacts cause premature wear which greatly reduces the life of themechanism. Hard, durable metal parts are therefore normally required toretard wear at the point of impact. Moreover, precautions must be takento protect the remainder of the switch from the effects of the shockcreated by the impact. In addition, the vibration and noise produced ishighly objectionable in many applications.

It is accordingly a further object of the present invention to absorbthe kinetic energy of the moving parts of a stepping switch without theusual, undesirable impact effects.

It -is a related object of the present invention to increase theoperating life of an electromagnetically operated stepping switch.

The stop member employed in prior overtravel control schemes must beaccurately positioned, often within a few thousandths of an inch, tostop forward motion at precisely the proper point, neither too soon nortoo late in the stroke, and at a time when the velocity of the movingparts is at its maximum value. This critical adjustment must be made byskilled manufacturing personnel, greatly increasing the cost of theswitch assembly operation, and consequently tending to limit production.

It is accordingly a further object of the present invention to reducethe cost of manufacturing quality stepping 3,422,691 Patented Jan. 21,1969 switches by eliminating the necessity for critical adjustments inthe overtravel control mechanism for such a switch.

When conventional overtravel control schemes are employed, the switchbecomes locked in position whenever the driving magnet is continuouslyenergized. The pawl becomes locked against the overtravel stop and,being in engagement with the ratchet wheel, in turn locks this wheel inposition. It is often desirable, however, to manually (or otherwise)operate the switch by turning the ratchet wheel in the forward directioneven though the driving magnet is energized.

It is accordingly a further object of the present invention to permitthe switch to be advanced while the driving pawl is in its operatedposition.

In a principal aspect, the present invention takes the form of animproved overtravel control mechanism for an electromagnetic steppingswitch. According to a principal feature of the invention, a springloaded catching member is employed to intercept the pawl as it iscarried in an arcuate path by the racthet wheel. After engagement, thespring load catching member operates to retard further motion of boththe pawl and the ratchet. By eliminating the usual high pressure impactat the end of the stroke, wearing is reduced, thus permitting the use ofan impact absorbing material for the catching member which thus providesstill softer operation.

These and other objects, features and advantages of the presentinvention will become more apparent through a consideration of thefollowing detailed description. Dur ing the course of this description,reference will frequently be made to the attached drawing in which:

FIGURE 1 is a perspective view of an electromagnetic stepping switchembodying the principles of the invention;

FIGURE 2 is an end view of the switch shown in FIG- URE 1;

FIGURES 2A-2D are enlarged end views of the ratchet wheel, pawl andcatching member shown in a sequence of positions during the course ofthe operation of the switch;

FIGURE 2E is a partial end view of the stepping switch as shown inFIGURE 2 illustrating the manner in which the catching member may befully deflected to provide manual override capability;

FIGURE 3 is a side view of the stepping switch shown in FIGURES l and 2;and

FIGURE 4 is a top view of the stepping switch shown in FIGURES l, 2 and3.

The electromagnetically operated stepping switch shown in perspective inFIGURE 1 includes an electromagnet indicated generally at 11 mounted ona frame indicated generally at 14. The frame 14 is shaped to provide apair of upwardly extending flanges at 16 and 17 as well as threedownwardly and outwardly extending mounting lugs, two of which are seenat 18 and 19 in FIGURE 1. The third mounting lug 20 is shown in the topview of FIGURE 4.

The magnet 11, when energized, pulls against an armature indicatedgenerally at 22. The armature 22 is mounted for pivotal movement aboutthe upper edge of flange 16 and is held in place by a projection 23which extends upwardly from the top of the flange 16 through a slot inarmature 22. When the magnet 11 is de-energized, a spring 25 holds thearmature 22 in spaced relation from the magnet 11. Spring 25 isconnected between a rearwardly projecting lug 27 bent outwardly from themount- 3 ing frame 14and rearwardly projecting lug 29 on the armature22. A pawl 30 is pivotally mounted on the armature 22 by means of afastening pin 32. A bridge member 33 affixed to the forward end ofarmature 22 surrounds the pawl 30 yet permits the pawl 30 to pivotlaterally about pin 32.

When the electromagnet 11 is energized, the armature 22 is pulled in toforce pawl 30 downward to a position of first engagement with a ratchetwheel indicated generally at 35. A spring 37 coupled between the end ofpawl 30 and a lug 38 on the upwardly extending flange 17 biases pawl 30laterally toward the ratchet wheel 35. The forward end of pawl 30 isinserted through an opening 34 in flange 17 and into a rectangularwindow 39 defined by a catching member 40. The catching member 40 ispivot-ally mounted about a pin 41 through the flange 17. In FIGURE 1, aportion of the flange 17 is cut away to better illustrate the positionand shape of the catching member 40.

As clearly seen in FIGURE 2 of the drawings, a coil spring connectedbetween an upwardly projecting lug 42 on the catching member 40 and alug 43 on flange 17 normally holds catching member 40 against aneccentric stop member 44 which is held flush against the flange 17 bymeans of a screw 46. By loosening screw 46 and rotating the eccentricstop member 44, the rest position of the catching member 40 may bequickly and accurately adjusted.

As illustrated by FIGURES 2A-2D, the rectangular window 39 in catchingmember 40 serves to guide the pawl 30 into engagement with theappropriate tooth in ratchet wheel 35 and, near the end of the stroke,intercepts the pawl 30 to retard further motion of both the pawl 30 andthe ratchet wheel 35. As seen in FIGURE 2A, the forward end of the pawl30 is precisely located in its rest position at the upper inside cornerof the window 39, the pawl 30 being held against inside wall 47 ofwindow 39 by spring 37. As the magnet 11 is energized, the pawl 30 isforced downward and is guided by the inside wall 47 to a position offirst engagement with the ratchet wheel 35. Further downward motion ofthe pawl 30 causes the ratchet wheel 35 to rotate and imparts lateralmotion to the pawl 30 (from right to left in FIGURE 2). At the positionshown in FIGURE 20, the pawl 30 is wedged between the outer wall 48 ofwindow 39 and the shoulder surface 50 defined by one tooth of theratchet wheel 35. The catching member 40 thus serves to intercept thepawl 30 and acts through the pawl 30 to retard further motion of theratchet wheel 35. Since the catching member 40 is pivotally mounted andspring loaded by spring 41, the window 39 in catching member 40 ispermitted to move (to the left as seen in FIGURE 2) to some extent toallow the kinetic energy of the pawl and ratchet wheel to be graduallyabsorbed without pronounced impact. FIG- URE 2D of the drawings showsthe catching member 40 at the point of greatest deflection. Thereafter,the spring 41 tends to return the catching member 40 to its originalposition, also forcing the ratchet wheel 45 to return to its desiredlocation from the overthrown position shown in FIGURE 2D.

The ratchet wheel 35 is further located by means of a conventionalspring loaded ball detent arrangement comprising a leaf spring 51 and ametal ball 53 which is held within a collar 54. The leaf spring 51 isfixedly mounted to the frame 14 by means of a screw 56 (which alsomounts the magnet 11 to the frame 14). Leaf spring 51 forces the ball 53upward into the notch separating adjacent teeth on the underside of theratchet wheel 35 as shown in FIGURE 2.

The ratchet wheel 35, which is preferably constructed of a low frictionplastic, such as Delron (acetol resin) or Lexan (polycarbonate resin),rotates a shaft 60 journaled to the flange 17 by means of a mountingbarrel indicated at 63. The armature 60 is held in place by means of aspring clip 65 which engages with a peripheral groove in 4 the shaft 60and which is separated from the barrel 63 by means of a low frictionwasher of Delron or Lexan.

As will be readily appreciated by those skilled in the art, a secondpawl or dog may be employed in conjunction With the ratchet wheel 35 toprevent the rotation of the ratchet 35 and shaft 60 in the reversedirection. In addition, electrical contact blades associated witharmature 22 or ratchet 35 may be positioned to open at a precise pointin the stroke.

As clearly seen from FIGURE 2C of the drawings, when the electromagnet11 is continually energized, the pawl 30 is held in a lockedrelationship between the catching member 40 and the ratchet wheel 35,preventing rotation of the ratchet wheel 35 in either direction. Inorder to permit the ratchet wheel 35 to the manually advanced by forcedrotation of the shaft 60, the catching member 40 contemplated by theinvention deflects to an extreme position as shown in FIGURE 2E of thedrawings allowing the teeth on ratchet wheel 35 to bypass the pawl 30.

The novel overtravel control mechanism contemplated by the presentinvention may also be used in conjunction with known indirect actingstepping switches; that is, switches in which the ratchet is advancedwhen the magnet is de-energized.

It is to be understood that the embodiment of the invention which hasbeen described is merely illustrative of one application of theprinciples of the invention. Numerous modifications may be made by thoseskilled in the art without departing from the true spirit and scope ofthe invention.

What is claimed is:

1. In a stepping relay having a ratchet wheel and an electromagneticallydriven pawl which engages with and advances said wheel, said pawl beingcarried in an arcuate path as said wheel is advanced, improvedovertravel control mechanism which comprises a spring loaded catchingmember positioned to intercept said pawl at a predetermined point and tothereafter retard further motion of said pawl along said arcuate path.

2. An improved overtravel control mechanism as set forth in claim 1including means for adjusting the position of said predetermined pointof interception.

3. An improved overtravel control mechanism as set forth in claim 1wherein said catching member acting through said pawl retards thefurther motion of said ratchet wheel after said pawl passes saidpredetermined point of interception.

4. An improved overtravel control mechanism as set forth in claim 1wherein said catching member is mounted on said relay for pivotal motionin a plane substantially perpendicular to the axis of rotation of saidratchet wheel.

5. An improved overtravel control mechanism as set forth in claim 4wherein said catching member is normally spring loaded against a stopmember adjustably mounted on said relay.

6. In a stepping relay having a ratchet wheel, a pawl, and anelectromagnet for driving said pawl in a first direction to engage withnotches in said wheel and to advance said wheel by an incrementalamount, said pawl being carried in an arcuate path by said wheel afterengagement thereby imparting motion to said pawl in a second directionperpendicular to said first direction,

an improved overtravel control mechanism which comprises a spring-loadedcatching member positioned to intercept said pawl at a predeterminedpoint along said arcuate path and to thereafter retard further motion ofsaid pawl in said second direction.

7. An improved overtravel control mechanism as set forth in claim 6wherein said spring loaded member acts against said wheel through saidpawl to retard further motion of said wheel after said pawl has passedsaid predetermined point of interception.

3. An improved overtravel control mechanism as set forth in claim 7wherein said spring loaded member com- 5 6 prises an elongated membermounted on said relay for References Cited pivotal motion in a planesubstantially perpendicular to UNITED STATES PATENTS the axis ofrotation of said wheel, said member having an aperture therein forreceiving said pawl, said aperture be- 2,150,680 3/1939 Fuller 74 142ing defined by a first and second opposing and substan- 2,990,723 7/1961Holpuch 74 142 5 3,106,849 10/1963 Valleau 74142 tially parallel sidewalls, said pawl being normally spring loaded against said first sidewall such that said first side wall serves to guide said pawl from itsrest position to a FRED MATTERN lma'y Exammer' position of engagementwith said ratchet wheel. WESLEY S. RATTIFF, Assistant Examiner.

1. IN A STEPPING RELAY HAVING A RATCHET WHEEL AND AN ELECTROMAGNETICALLYDRIVEN WHICH ENGAGES WITH AND ADVANCES SAID WHEEL, SAID PAWL BEINGCARRIED IN AN ARCUATE PATH AS SAID WHEEL IS ADVANCED, IMPROVEDOVERTRAVEL CONTROL MECHANISM WHICH COMPRISES A SPRING LOADED CATCHING